Biochemical studies on rat brain tissues during postnatal growth

Abstract

Wistar rats were used without sex discrimination in these studies. Rats of a family derived from same parent were devided into 5 groups such as 1st week-, 2nd week-, 3rd week-, 4th week- and 8th week-postnatal age groups, consisted of 11 rats each Whole brain tissue homogenates were prepared without delay after removal.' of brains and were immediately subjected to varying biochemical assays. The variations were examined and discussed in the course of 8 weeks of postnatal age on the amounts of nucleic acids, protein, total free amino acids, acid amino acids and GABA, and the activities of RNase, RNase inhibitor, LDH, and GDA. The results obtained were summarized as follows. 1. Whole brain weight of rats showed a marked increase from 0.49 of first week age to 1. 4g of third week age , and steady but a much lesser increase thereafter until 8th week. 2. There occurred a marked decrease in brain DNA level at g wet weight tissue basis during first to third week after birth, followed by a slight decrease until 8th week postnatal age. Its ster decline was more notable during 2nd to 3rd postnatal week. There showed a slight but steady decrease in brain RNA level at g wet tissue basis in the course of 8 weeks after birth. But total DNA contents of whole brain tissue showed a marked increase during same period, but latter being more noticeable. 3. The brain protein content at g wet tissue basis increased markedly during first to third week after birth, showing same pattern of increase in whole brain weights. 4. The total free amino acid content tended to decrease at g wet tissue basis until 4th postnatal week from birth. The glutamic acid level was shown a marked rise until 4th week after birth, 239 showing just same trend of increase in whole brain weight and protein content. The contents of aspartic acid and GABA in brain tissue increased slightly during 3rd week after birth. 5. The total LDH activity in brain tissue increased until 3rd postnatal week , and the LDH isozyme pattern varied during 3 postnatal weeks, thus LDH 1 and LDH 2 isozyme activities showed a sharp increase during first to third week after birth, whereas the isozymes activities of LDH 5 and LDH 4 showed a decrease during same period. 6. The activity of free alkaline RNase in brain tissue decreased sharply during first to fourth week after birth, followed by a slight increase at 8th week. In contrast, the RNase inhibitor activity showed no variation during experimental period. 7. The activity of GDA in brain tissue showed no marked change except its increase at 2nd week during the same period coinciding with the most marked variation of nucleic acids